Can I POST data with python requests lib with http-gzip or deflate compression?

Question

I use the request-module of python 2.7 to post a bigger chunk of data to a service I can't change. Since the data is mostly text, it is large but would compress quite well. The server would accept gzip- or deflate-encoding, however I do not know how to instruct requests to do a POST and encode the data correctly automatically.

Is there a minimal example available, that shows how this is possible?

Answer 1

# Works if backend supports gzip

additional_headers['content-encoding'] = 'gzip'
request_body = zlib.compress(json.dumps(post_data))
r = requests.post('http://post.example.url', data=request_body, headers=additional_headers)

Answer 2

I can't get this to work, but you might be able to insert the gzip data into a prepared request:

#UNPROVEN
r=requests.Request('POST', 'http://httpbin.org/post', data={"hello":"goodbye"})
p=r.prepare()
s=StringIO.StringIO()
g=gzip.GzipFile(fileobj=s,mode='w')
g.write(p.body)
g.close()
p.body=s.getvalue()
p.headers['content-encoding']='gzip'
p.headers['content-length'] = str(len(p.body))  # Not sure about this
r=requests.Session().send(p)

Answer 3

The accepted answer is probably wrong due to incorrect or missing headers:

additional_headers['content-encoding'] = 'gzip'
request_body = zlib.compress(json.dumps(post_data))

Using the zlib module's compressobj method that provides the wbits argument to specify the header format should work. The default value is MAX_WBITS=15 which means zlib header format. This is correct for Content-Encoding: deflate. For the compress method this argument is not available and the documentation does not mention which header (if any) is used unfortunately.

For Content-Encoding: gzip wbits should be something between 16 + (9 to 15), so 16+zlib.MAX_WBITS would be a good choice.

I checked how urllib3 decodes the response for these two cases and it implements a try-and-error mechanism for deflate (it tries raw and zlib header formats). That could explain why some people had problems with the solution from the accepted answer which others didn't have.

---

tl;dr

gzip

additional_headers['Content-Encoding'] = 'gzip'
compress = zlib.compressobj(wbits=16+zlib.MAX_WBITS)
body = compress.compress(data) + compress.flush()

deflate

additional_headers['Content-Encoding'] = 'deflate'
compress = zlib.compressobj()
body = compress.compress(data) + compress.flush()

Answer 4

I've tested the solution proposed by Robᵩ with some modifications and it works.

PSEUDOCODE (sorry I've extrapolated it from my code so I had to cut out some parts and haven't tested, anyway you can get your idea)

additional_headers['content-encoding'] = 'gzip'
s = StringIO.StringIO()
g = gzip.GzipFile(fileobj=s, mode='w')
g.write(json_body)
g.close()
gzipped_body = s.getvalue()
request_body = gzipped_body

r = requests.post(endpoint_url, data=request_body, headers=additional_headers)

Answer 5

For python 3:

from io import BytesIO
import gzip

def zip_payload(payload: str) -> bytes:
    btsio = BytesIO()
    g = gzip.GzipFile(fileobj=btsio, mode='w')
    g.write(bytes(payload, 'utf8'))
    g.close()
    return btsio.getvalue()

headers = {
    'Content-Encoding': 'gzip'
}
zipped_payload = zip_payload(payload)
requests.post(url, zipped_payload, headers=headers)

Answer 6

I needed my posts to be chunked, since I had several very large files being uploaded in parallel. Here is a solution I came up with.

import requests
import zlib

"""Generator that reads a file in chunks and compresses them"""
def chunked_read_and_compress(file_to_send, zlib_obj, chunk_size):
    compression_incomplete = True
    with open(file_to_send,'rb') as f:
        # The zlib might not give us any data back, so we have nothing to yield, just
        # run another loop until we get data to yield.
        while compression_incomplete:
            plain_data = f.read(chunk_size)
            if plain_data:
                compressed_data = zlib_obj.compress(plain_data)
            else:
                compressed_data = zlib_obj.flush()
                compression_incomplete = False
            if compressed_data:
                yield compressed_data

"""Post a file to a url that is content-encoded gzipped compressed and chunked (for large files)"""
def post_file_gzipped(url, file_to_send, chunk_size=5*1024*1024, compress_level=6, headers={}, requests_kwargs={}):
    headers_to_send = {'Content-Encoding': 'gzip'}
    headers_to_send.update(headers)
    zlib_obj = zlib.compressobj(compress_level, zlib.DEFLATED, 31)
    return requests.post(url, data=chunked_read_and_compress(file_to_send, zlib_obj, chunk_size), headers=headers_to_send, **requests_kwargs)

resp = post_file_gzipped('http://httpbin.org/post', 'somefile')
resp.raise_for_status()